It has been reported that prostaglandin E2 (PGE2) had anti-inflammatory and analgesic effects, although it was well known that PGE2 combined with bradykinin (BK) showed proinflammatory and algesic effects. On the other hand, it has recently been known that BK showed an indirect activating effect on cathepsin B, a lysosomal enzyme, which may be mediated through calcium ion-dependent steps, followed by production of enkephalins (EK), endogenous anti-inflammatory and analgesic peptides, in the rat incisor pulp. The purpose of the present study is to examine whether PGE2 could have an effect on activation or release of cathepsin B in the pulp tissue, or not. Intact whole pulps of the rat incisors were incubated with N alpha-benzoyl-arginine-beta-naphthylamide (BANA), a substrate for cathepsin B, in the presence or absence of BK and PGE2 in Hanks solution (pH 7.4), in order to determine the BANA-degrading activity and EK producing activity. Both hydrocortisone and lidocaine which were stabilizers for lysosomal membrane markedly inhibited the BANA-degrading activities in the presence of BK, and in contrast, retinol, a labilizer for lysosomal membrane, significantly enhanced the BK-induced BANA-degrading activity. PGE2, like hydrocortisone and lidocaine, inhibited the BANA-degrading activity, in a dose-dependent manner, regardless of the presence or absence of BK, as well as resulted in a decrease of EK production in the pulp. Furthermore, both arginine, a cleavage product of BK by carboxypeptidase B, and arachidonic acid, which were endogenous activators for soluble guanylate cyclase, enhanced the BANA-degrading activity in the pulp homogenate.(ABSTRACT TRUNCATED AT 250 WORDS)